Power operated gripper

ABSTRACT

A power operated gripper in which both the gripping and releasing movements of the gripping elements are made under power. The gripper comprises a thrust member which is extended and retracted in a linear motion by the power means, gripper arms which swing in an arc to grip and release a workpiece, a cam and roller structure to convert the linear motion of the thrust member to arcuate movement of the gripper arms and adjusting screws which engage the walls of a V-shaped groove in the thrust member to control the extent of its movement in each direction. The parts are constructed and arranged to permit adjustment of the gripper while it is operating so that precise control of the gripping and releasing motion of the gripper arms may be attained under actual operating conditions.

BACKGROUND OF THE INVENTION

This invention relates to apparatus for gripping a work piece which isto be moved or worked on by a remotely operated or automaticallyoperated machine. This is the area of art commonly referred to as"robotics."

It is common in this field to grip a work piece externally or internallyby means of a gripper actuated by a power device such as a hydraulic orpneumatic cylinder, solenoid or the like. This operation is commonly ofa repetitive nature in which identical work pieces are operated on bythe gripper in succession. The force applied by the gripper to the workpiece must be adequate to hold it firmly but in many operations it isimportant that the gripper not deform or mar the work piece. Therefore,the ability of the gripper to adjust to a precise aperture and tomaintain the adjustment over a series of successive operations iscritical. However, with most devices in the prior art, the adjustmentmust be done by trial and error. That is, the initial adjustment is madeby measurement or estimate with the gripper stationary or inoperative.Then the gripper is tried, readjusted as necessary and tried again andso forth. Because of the location or nature of the adjusting means,grippers of the prior art cannot be adjusted while they are actually inoperation. Therefore, a precise adjustment, taking into account freeplay, backlash and other relevant factors, cannot be made.

SUMMARY OF THE INVENTION

The present invention provides a gripper in which a precise adjustmentof the gripper can be made while it is actually in operation and theeffect of the adjustment seen in the operation of the gripper while itis operating.

The invention comprises apparatus in which a plunger attached to a powerpiston is extended and/or retracted by movement of the piston in onedirection or the other or both under the influence of a pressure fluidelectrical apparatus or other power means. Linear movement of theplunger is converted to swinging action of gripper jaws which areeffective to grip and hold the external or internal surface of a workpiece. The plunger reciprocates inside a housing which remainsstationary during movement of the piston and the gripper jaws.Adjustment of the gripper jaws is by means of set screws located on thehousing and accessible from the exterior thereof while the gripper isoperating. The set screws engage the walls of a V-notch orcircumferential groove in the plunger. Adjusting the set screw inwardreduces the clearance between the set screw and the corresponding wallof the notch in the plunger and consequently limits the linear travel ofthe plunger. This ultimately also limits the swinging motion of thegripper arms. Two set screws may be provided, one to control extensionof the plunger and one to control its retraction. In turn, this willcontrol the opening of the jaws to grip the interior surface of a workpiece and the closing motion of the jaws to grip the exterior surface ofa work piece.

To simplify the construction and manufacture, a suitable V-grooveextending completely around the circumference of the plunger and ofsufficient width to provide adjustment for the full range of motion ofthe plunger is provided. On smaller sizes of the gripper, however, sucha groove may weaken the structure of the plunger. In those cases,separate notches are provided for adjusting inward and outward movementof the plunger, each of said notches extending only partially around thecircumference of the plunger.

Any of various well known and suitable means may be provided forconverting the reciprocating action of the plunger to swinging movementof the gripper arms or jaws. Cam and roller means are illustratedherein.

It is an object of the present invention to provide a gripper forgripping the internal or external surfaces of a work piece in whichadjustment of the opening or closing motion of the gripper arms can bemade while the gripper arms are being operated.

It is another object of the invention to provide such a gripper in whichadjustment of the gripping action of the arms or jaws can be made simplyand easily in such a manner as to account for backlash, wear and otherpractical factors which cannot be accounted for by adjustment madesolely on the basis of measurement.

These and other objects, features and advantages of this invention willbecome apparent from the following description in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the invention.

FIG. 2 is a view of the invention taken in the direction of the arrowsand along the line 2--2 in FIG. 1.

FIG. 3 is a drawing of an optional form of the plunger.

FIG. 4 is a top view of the invention.

DETAILED DESCRIPTION

To illustrate a complete operating device the gripper is shown poweredby a double acting pneumatic cylinder. However, it must be understoodthat any of various well known power means may be used to operate thegripper. For example, the power means may be pneumatic, hydraulic,electrical or any other type. It may be double acting, as illustrated orsingle acting or single acting with spring return. The type or form ofpower means is in no way to be considered a limitation of the invention.

Referring now to the drawings, the gripper 1 of the invention is shownas comprising a double acting cylinder 2 attached to a gripper armhousing 26 of generally cylindrical form and a pair of gripper arms 14and 15 actuated by a plunger 5. The cylinder may be any of variousreadily available devices of this type. For illustration it is shown asa short stroke large diameter cylinder comprising a cylinder housing 6having a bottom cover 17 and a top cover 18, piston 3 having a seal ring4 and a piston rod 16 extending out of the top cover 18 through abearing sleeve 20 having a piston rod seal ring 25. Top and bottomcovers 17, 18 are attached to the housing 6 and sealed thereto toprevent the escape of pressure fluid by suitable means such as screwsand O-rings, not shown. Cylinder 2 is removably secured to gripper armhousing 26 by suitable means such as screws, not shown. Inlet ports 22and 23 are provided to admit pressure fluid to chamber 24 to drive thepiston in a downward direction or in an upward direction as viewed inFIG. 1. Piston rod 16 is secured to a plunger or thrust member 5 ofgenerally cylindrical configuration by suitable means. For example,piston rod 16 may be provided with a threaded stud and thrust member 5may have an internally threaded bore which engages the stud. Suchconnecting means are common and well known and are not shown.

Thrust member 5 reciprocates within a bore 43 in gripper arm housing 26.Bore 43 may be provided with a bearing sleeve 19 to reduce friction.

Gripper arms or jaws 14 and 15 are provided to hold a work piece. Thegripper arms have inner gripping portions 27 and 28 respectively andouter gripping portions 29 and 30. Each of the gripper arms has a bore33 of a size to receive pivot pins 21. Gripper arms 14 and 15 aremounted for pivotal movement on pivot pins 21 within a slot 46 in thefree end of housing 26. Slot 46 mates and is in alignment with slot 37in the plunger 5. Pivot pins 21 are mounted in bores 38 in gripper armhousing 26 and are retained therein by suitable means such as C-washers39. A roller cam 10 is mounted in a slot 37 in the free end of plunger 5for rotational motion on a roller rod or spindle 11. Roller spindle 11extends through the roller cam and through bores 40 in the distal end ofthe plunger 5.

Arms 14 and 15 have arcuate cam surfaces 31 and 32 respectively whichengage the outer surface of the roller 10. It can be seen that asplunger 5 and roller cam 10 move linearly in response to movement ofpiston 3 and piston rod 16, arms 14 and 15 will be pivoted inwardly andoutwardly by the action of roller cam 10 against cam surfaces 31 and 32.The gripping surfaces 27 and 28 will move inwardly toward each otherupon movement of plunger 5 in a downward direction to grip the exteriorsurfaces of a work piece. Gripping surfaces 29 and 30 will move in anoutward direction of grip the internal surface of a hollow work pieceupon movement of the plunger 5 in an upward direction. Pivotablemovement of the arms 14 and 15 will be relative to the linear movementof the plunger 5. Therefore, the extent of movement of the arms and theforce applied to a work piece can be controlled by adjusting the linearmotion of the plunger. In the invention this is accomplished by themeans described below.

Plunger 5 is provided with a circumferential V-notch or groove 9.Threaded bores 41 and 42 are provided extending through the housing 26and the sleeve 19. Set screw 7, having a tapered end 12, is threadedinto the bore 41 and a set screw 8, having a tapered end 13, is threadedinto the bore 42. Bores 41 and 42 are offset from each other verticallyso that set screw 7 will contact the upper part of the V-notch and setscrew 8 will contact the lower portion of the V-notch. As set screw 7 isadjusted inward it will limit the downward travel of plunger 5 and,therefore, the closing action of the gripping portions 27 and 28 on awork piece. As set screw 8 is adjusted inward, it will limit the upwardtravel of plunger 5 and, therefore, the gripping action of portions 29and 30 on the interior of a work piece. When a work piece is beinggripped on its external surfaces by portions 27, 28 adjustment of setscrew 7 will also limit the return action or opening of the grippingsurfaces 27 and 28 to release the work piece. Similarly, adjustment ofset screw 8 will limit the opening or releasing action of grippingportions 29 and 30. The screw threads on screws 7 and 8 or on bores 41and 42 or both may be of the locking type so that the screws willmaintain their adjusted positions. The location of adjusting screws 7and 8 on the gripper arm housing has a very important advantage. Itpermits the opening and closing action of gripper arms 14 and 15 to beadjusted while the gripper is being operated in the mode and with thework piece for which the gripper is being adjusted. This permits preciseadjustment to control very closely the pressure applied to a work pieceso that it may be held as tightly as necessary to permit the desiredoperation, but so that marring or deformation does not occur. Byadjusting the return action of the jaws to release the work piece aswell as the gripping movement, the required movement of piston 3 can bereduced to a minimum and the use of pressure fluid or other power sourceheld to a minimum. This results ultimately in lower use of energy and asubstantial cost savings.

FIG. 3 shows a modified form of the plunger or thrust member which isparticularly useful in smaller versions of the gripper. In this versionthe thrust member 34 is formed with two separate notches 35 and 36extending around only a small portion of the circumference of the thrustmember. The notches are offset vertically from each other so that theirinnermost tips 44 and 45 are not in alignment with each other. Thismeans that a greater cross-section of the thrust member 34 remains andthe strength of the member is preserved.

It is obvious to those skilled in the art that although the inventionhas been shown and described in a limited number of preferredembodiments many variations may be made in the form and structure herepresented without departing from the scope of the present invention asset forth in the appended claims.

What is claimed is:
 1. A power actuated gripper comprising a housingwhich remains stationary during operation of the gripper, a thrustmember constructed and arranged for linear reciprocating motion in saidhousing, a pair of gripping arms arranged for swinging motion controlledby said thrust member, power means having a stationary member connectedto said housing and a movable member connected to said thrust member,cooperating adjusting means on said housing and said thrust memberconstructed and arranged to limit linear movement of said thrust memberin at least one direction, said cooperating adjusting means includingadjustable means on said housing, said adjustable means being adjustablewhile the gripper is operating by virtue of being on said housing whichremains stationary, whereby adjustment of the motion of said grippingarms may be made under actual working conditions.
 2. A power actuatedgripper as set forth in claim 1 wherein said adjusting means areeffective to limit linear movement of the thrust member in both of itsdirections of movement.
 3. A power actuated gripper as set forth inclaim 1 wherein said cooperating adjusting means include a screw and aV-groove.
 4. A power actuated gripper as defined in claim 2 wherein saidadjustable means comprise two screws, one of said screws being effectiveto limit movement of the thrust member in one direction and the other ofsaid screws being effective to limit movement of the thrust member inthe other direction.
 5. A power actuated gripper as set forth in claim 1wherein said gripping arms are mounted on said stationary housing forswinging movement toward and away from each other, and further includingcam means interconnecting said thrust member and said pair of f armswhereby reciprocating movement of the thrust member is converted toswinging movement of said arms to grip and release a work piece.
 6. Apower actuated gripper as set forth in claim 5 wherein said cooperatingadjusting means include a screw and a V-groove effective to controlmovement of the thrust member in one direction and a screw and aV-groove effective to control movement of said thrust member in theother direction.
 7. A power actuated gripper for repetitively andconsecutively gripping and releasing work pieces of identical size andshape, said gripper including a stationary housing, a thrust memberconstructed and arranged for linear reciprocating movement in saidhousing, power means for moving said thrust member, a pair of armsconstructed and arranged for swinging motion toward each other forgripping a work piece and away from each other to release a work piece,swinging motion of said gripping arms being controlled by linearmovement of said thrust member, cooperating adjusting means on saidhousing and said thrust member to adjustably limit the linear movementof said thrust member in at least the direction in which it controlsmotion of the gripping arms toward each other, said adjusting meanscomprising a screw on said housing which is readily adjustable while thegripper is operating repetitively to grip and release a work piece byvirtue of its location on the housing which is stationary, wherebyadjustment of the adjusting means to apply the desired gripping force toa work piece can be made with precision under actual operatingconditions.